Plate heater for a manifold of an injection molding apparatus

ABSTRACT

An injection molding apparatus includes a manifold having a manifold channel for receiving a melt stream of moldable material and delivering the melt stream to a mold cavity through a nozzle channel of a nozzle and a mold gate. A heater is coupled to the manifold. The heater includes a heater plate that is formed by an extrusion process and at least one channel for receiving a heating element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/279,537filed Aug. 14, 2008, now U.S. Pat. No. 7,806,681, which is a nationalstage application under 35 U.S.C. §371 of PCT/CA07/00226 filed Feb. 15,2007, which claims foreign priority to U.S. application Ser. No.11/354,416 filed Feb. 15, 2006, now abandoned, each of which isincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to an injection moldingapparatus and, in particular to a plate heater for a manifold.

BACKGROUND OF THE INVENTION

As is well known in the art, a typical multi-cavity hot runner injectionmolding system includes a heated manifold for conveying a pressurizedmelt stream from an inlet to a plurality of outlets. A heated nozzlecommunicates with each outlet to deliver the melt to a respective moldcavity through a mold gate. Manifolds have various configurationsdepending on the number and arrangement of the mold cavities.

Different heating arrangements are known for heating manifolds. A commonarrangement is an electrical heating element that is received in agroove in a manifold outer surface, as described in U.S. Pat. No.4,688,622 to Gellert, which issued Aug. 25, 1987. Other arrangementsinclude cartridge heaters that are cast into the manifold as describedin U.S. Pat. No. 4,439,915 to Gellert, which issued Apr. 3, 1984, andplate heaters with cast-in heaters that are secured along the surface ofthe manifold, as described in U.S. Pat. No. 5,007,821 to Schmidt, whichissued Apr. 16, 1991. Manufacture and assembly of each of these heatingarrangements requires machining of the manifold, the heater or both,which can be both costly and time consuming.

For certain large molded parts that require melt delivered from largeheated manifolds, the melt stream is heated by either multiple smallerheater plates attached to the manifold or heater elements pressed withingrooves machined into the manifold surface. Each of these solutions hasits benefits and limitations.

Heater plates provide more consistent heat distribution than a heaterelement in contact with the manifold surface. Further, heater plates mayinclude more than one heater element allowing for redundancy. However,heater plates are typically made by investment casting methods, whichdoes not accommodate the manufacture of larger plates due to warpage andbending that occurs as the plates get longer. Therefore, multipleshorter plates, i.e., plates typically less than 170 mm, are utilizedfor larger manifold applications, which require more control zones tooperate. Further, heater elements of current heater plates are castwithin the heater plate and cannot be replaced once they fail, so thatthe entire heater plate must be replaced upon failure of the heaterelements therein.

Alternatively, heater elements that are pressed-in machined grooves onthe surface of a manifold may be removed for replacement, althoughmachining such grooves is time consuming and expensive. In addition,redundancy is provided for by machining a corresponding groove in anopposing surface of the manifold and pressing a secondary heater elementinto the second groove, adding to the time and cost associated with thisproduction method.

Accordingly, what is needed is a manifold heater arrangement thatprovides the improved heat distribution and redundancy of a heater plateand provides for replacement of failed heater elements and fewer controlzones. In addition, a heater plate that may be efficiently constructed,particularly at longer sizes, is desired.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention there is provided aninjection molding apparatus including a heated manifold with a meltchannel for transferring molten material from an injection moldingmachine to one or more hot runner nozzles which in turn inject themolten material to one of more cooled mold cavities to form a plasticpart. One or more heaters are connected to the manifold in aconfiguration to provide heat to maintain the temperature of the moltenmaterial throughout the entire length of the melt channels in themanifold. The plate heater includes a heater plate body and at least twoheating elements. A surface of the heater plate body has at least twochannels therein and each heating element is received within arespective channel. At least one end cap is provided for commonly fixingterminal ends of at least two of the heating elements relative to theheater plate body.

Another embodiment of the present invention includes a method ofmanufacturing a plate heater for a hot runner manifold. The methodincludes providing an extruded bar like blank having at least twostraight longitudinal grooves therein; planning a flat contact face ofthe blank; machining the grooves to fine forming straight longitudinalchannels in the blank to gain a heater plate body; insertinglongitudinal heating elements into the longitudinal channels in theheater plate body.

Further advantageous embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings in which like referencenumerals indicate similar structure. The drawings are not to scale.

FIG. 1 is a side sectional view of an injection molding apparatusaccording to an embodiment of the present invention.

FIG. 2 is an isometric view of a portion of the injection moldingapparatus of FIG. 1.

FIG. 3 is a top view of a plate heater of the injection moldingapparatus of FIG. 2.

FIG. 4 is an isometric view of the heater of FIG. 3.

FIG. 5 is a cross-section along line 5-5 of the heater plate of FIG. 3with the heating elements removed.

FIG. 5A is a profile of an extruder die used to produce thecross-section of the heater plate body shown in FIG. 5.

FIG. 6 is an isometric view of an injection molding apparatus accordingto another embodiment of the present invention.

FIG. 7 is an isometric view of a plate heater according to anotherembodiment of the present invention.

FIG. 8 is an isometric view of a plate heater according to anotherembodiment of the present invention.

FIG. 9 is an isometric view of a portion of the plate heater shown inFIG. 8.

FIG. 10 is a cross-section along line 10-10 of the heater plate body ofFIG. 9 with the heating elements removed.

FIG. 10A is a profile of an extruder die used to produce thecross-section of the heater plate body shown in FIG. 10.

FIG. 11 is a top view of a plate heater according to another embodimentof the present invention.

FIG. 12 is a cross-section along line 12-12 of the plate heater shown inFIG. 11.

FIG. 13 is a perspective view of a plate heater according to anotherembodiment of the present invention.

FIG. 13A is an isometric view of a portion of the plate heater shown inFIG. 13.

FIG. 13B is a cross-section along line 13-13 of a heater plate body inaccordance with another embodiment of FIG. 13.

FIG. 14 is a perspective view of a plate heater according to anotherembodiment of the present invention.

FIG. 15 is a perspective view of the plate heater shown in FIG. 14 withone end cap taken away.

FIG. 16 is an enlarged view of the left end of the plate heater shown inFIG. 15.

FIG. 17 is an enlarged view of the left end of the plate heater shown inFIG. 15 with the cap clamp removed.

FIG. 18 is a view similar as in FIG. 17 with the lower half of the endcap attached.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an injection molding apparatus 10 is generallyshown. Injection molding apparatus 10 includes a manifold 12 having amanifold melt channel 14. Manifold melt channel 14 extends from an inlet16 to manifold outlets 18. Inlet 16 of manifold melt channel 14 receivesa melt stream of moldable material from a machine nozzle (not shown)through a sprue bushing 20 and delivers the melt to hot runner nozzles22, which are in fluid communication with respective manifold outlets18. Although a pair of hot runner nozzles 22 is shown in FIG. 1, it willbe appreciated that a typical injection molding apparatus may includeonly one or a plurality of hot runner nozzles for receiving melt fromrespective manifold outlets.

Each hot runner nozzle 22 is received in an opening 32 in a mold plate34. A collar 28 surrounds the nozzle 22. The collar 28 abuts a step 36,which is provided in opening 32 to maintain a nozzle head 26 of the hotrunner nozzle 22 in abutment with an outlet surface 40 of manifold 12. Anozzle tip 30 is received in a downstream end of hot runner nozzle 22and may be threaded thereto. A nozzle melt channel 24 extends throughhot runner nozzle 22 and nozzle tip 30. Nozzle melt channel 24 is incommunication with manifold outlet 18 to receive melt from manifoldchannel 14. Hot runner nozzle 22 is heated by a heater 54 and furtherincludes a thermocouple 56.

A mold cavity 50 is provided between mold plate 34 and a mold core 52.Mold cavity 50 receives melt from nozzle melt channel 24 through a moldgate 48. Cooling channels 58 extend through mold plate 34 to cool moldcavity 50.

Manifold 12 is maintained in position relative to mold plate 34 by alocating ring 46. Spacers 44 are provided between an inlet surface 38 ofmanifold 12 and a back plate 42. Referring also to FIG. 2, manifold 12is heated by heaters 60, which are coupled to the outlet surface 40 andside surfaces 62 of the manifold 12.

As shown in FIGS. 3-5, each plate heater 60 includes a heater plate body64 having flange portions 76 and base portions 78 that define a pair ofchannels 66 therebetween. Each channel 66 extends within a respectiveside surface 69 of heater plate 64. Although heater plate body 64 isshown having a pair of channels 66, the heater plate body 64 may beadapted to alternatively include one channel 66 or a plurality ofchannels 66.

The heater plate body 64 is formed by an extrusion process, as describedbelow, from a material that is more thermally conductive than themanifold 12, which is typically made from tool steel such as H13, P20 orSS420, for example. Suitable thermally conductive materials for heaterplate body 64 include aluminum, aluminum alloys, copper and copperalloys, such as brass and bronze. Alternatively, another suitablematerial may be used.

Channels 66 of heater plate body 64 are shaped and sized to receive andsecure heating elements (not shown) therein. As illustrated in FIG. 5, across-section of channel 66 may be described as key-shaped orbulb-shaped having a narrowed neck portion 71 and an enlarged cavityportion 67. In one embodiment, neck portion 71 is narrower than aheating element to be seated in cavity portion 67, wherein cavityportion 67 is sized to securely receive the heating element. Flangeportions 76, which form the upper surface of channels 66, and baseportions 78, which form the lower surface of channels 66, includeheating element retaining holes 74 for receiving fasteners (not shown)that force a mating surface 80 of flange portion 76 toward a surface 82of base portion 78 to impart a clamping force on the heating element.The clamping force increases the amount of contact, and therefore heattransfer, between the heating element and the heater plate body 64.

The plate heater 60 further includes relief holes 68, which are locatedat regular intervals along the length of the heater plate body 64. Therelief holes 68 are provided to receive mechanical items, includingfasteners (not shown), for coupling the plate heater 60 to the manifold12. A thermocouple aperture 70 extends through heater plate body 64 andreceives a thermocouple (not shown). Connectors 72, which allow theheating elements to communicate with a power source (not shown), arecoupled to the free ends of each of the heating elements. The heatingelements may be powered independently, in parallel or in series. Bypowering the heating elements independently or in parallel, a fail-safe,redundant arrangement is provided in which one plate heater willcontinue to provide heat even if the other heating element fails. In anembodiment where independent control of each heating element isprovided, an additional control zone and thermocouple are utilized.However in accordance with the present invention, regardless of how theplate heater is operated, the heating element(s) may be accessed forreplacement simply by removing the fasteners from retaining holes 74 andexposing/removing the heating element from channel 66.

In operation, melt is injected from the machine nozzle into manifoldchannel 14 of manifold 12 through sprue bushing 20. Nozzle melt channels24 of nozzles 22 receive melt from manifold outlets 18 and deliver themelt to mold cavities 50 through mold gates 48. Plate heaters 60 provideheat to the manifold 12 so that the melt flowing through the manifoldchannel 14 is maintained at a desired temperature. Once the moldcavities 50 have been filled with melt, the melt is cooled and themolded parts are ejected from injection molding apparatus 10.

Production of the heater plate body 64 will now be described. A billetof a selected material in a raw form is pushed through a dieincorporating the profile shown in FIG. 5A, to produce a heater platehaving the cross-section shown in FIG. 5. The die profile includes alinear portion 65′, which corresponds to a contact surface 65 on theheater plate body 64, and at least one extended portion 66′, whichcorresponds to channel 66 of the heater plate 64. The heater plate body64 is manufactured using an extrusion process, which includescold-working the initial extruded form. The cold-working of the extrudedplate makes it harder and stiffer than its cast counterpart, allowingfor improved performance with less warpage and bending. As such, alonger extruded heater plate body that is flatter and straighter than aplate produced by a casting process, for example, is achieved.

In one embodiment, a single extruded heater plate body may be later cutto produce a plurality of custom length heater plate bodies 64.Accordingly, following extrusion, heater plate body 64 is cut to adesired length, which is determined by the surface 40, 62 of themanifold 12 to which the plate heater 60 is to be coupled. Alsofollowing extrusion, contact surface 65 of the heater plate body 64 maybe machined by a machining process such as milling or grinding, forexample, in order to smooth out any imperfections resulting from theextrusion process. Machining of the contact surface 65 maximizes theamount of contact between the contact surface 65 and the surfaces 40, 62of the manifold 12 and therefore optimizes heat transfer therebetween.Relief holes 68 and thermocouple holes 70 are also machined into theheater plate body 64. Following machining, the heating elements arepositioned in the channels 66 and the fasteners are installed to clampthe heating elements in position. Once assembled, the plate heater 60 iscoupled to the manifold 12 and the heating elements are linked to thepower source.

The heating elements are removable from the channel 66 by unscrewing thefasteners to release the clamping pressure on the heating elements. Themanner in which the heating elements are secured allows them to bereplaced by an operator in the event that one or both of the heatingelements needs to be repaired or replaced. As such, the entire plateheater 60 does not need to be scrapped and replaced when one or moreheating elements fail, which provides a cost savings.

The plate heater 60 further provides some flexibility in that channels66 accommodate heating elements having different diameters. Inapplications where heating elements having smaller diameters areinstalled, it may be desirable to fill any gaps between the heatingelement and the channel 66 with a thermally conductive paste. Thethermally conductive paste does not affect the removal of the heatingelements 90 from the channels 66 and breaks away when the heatingelements are removed.

Referring to FIG. 6, an injection molding apparatus 10 a includes amanifold 12 a having a plate heater 60 a, which is similar to plateheater 60 of FIGS. 1-5. The plate heater 60 a is coupled to a frontsurface 84 of the manifold 12 a. As shown, the plate heater 60 a is theonly primary source of heat for the manifold 12 a. In anotherembodiment, the plate heater 60 a may be provided in combination withadditional plate heaters on the outlet and side surfaces 40 a and 62 aof the manifold 12 a, as shown in FIG. 1. The plate heater 60 a mayalternatively be provided in combination with a heater located on inletsurface 38 a, adjacent to sprue bushing 20 a. The plate heater 60 a mayalso be paired with another manifold heating method known in the art,such as an embedded heating element, a cartridge heater or a filmheater, for example. Operation of plate heater 60 a is similar tooperation of plate heater 60 of the previous embodiment and thereforewill not be described further here.

FIG. 7 shows another embodiment of a plate heater 60 b for heating amanifold. Plate heater 60 b is similar to the heaters 60, 60 a of theprevious embodiments; however, plate heater 60 b includes a centralaperture 86, which extends through plate heater 64 b. The centralaperture 86 is provided in order to allow a melt transporting, manifoldsupporting or manifold locating component to pass therethrough. The typeof component is determined by the location of the plate heater 60 b onthe manifold. For example, if the plate heater 60 b is located on aninlet surface of the manifold, a sprue bushing may extend through thecentral aperture 86, whereas if the plate heater 60 b is located on anoutlet surface of the manifold, a nozzle may extend through the centralaperture 86. Incorporating the central aperture 86 into the plate heater60 b increases the number of different locations at which the plateheater 60 b may be coupled to the manifold.

Referring to FIGS. 8-10, another embodiment of a plate heater 60 c for amanifold is shown. Plate heater 60 c includes a heater plate body 64 chaving channels 66 c provided in an upper surface 88 thereof. Heatingelements 90 are fully received within channels 66 c. Similar to channels66 of the embodiment of FIG. 5, channels 66 c are key-shaped to includea narrowed portion 71 c and an enlarged portion 67 c, as shown in FIG.10. Accordingly, heating elements 90 sit below heater plate uppersurface 88 in contact with substantially the entire surface of enlargedportion 67 c to provide for optimal heat transfer therebetween. Asshown, a longitudinal length of each heating element 90 is generallyarranged in a U-shape and includes an elbow 92 at one end and terminalends 94 at an opposite end. The terminal ends 94 of each heating element90 communicate with a power source (not shown) through a connector (notshown). Suitable materials for heater plate body 64 c are the same ashave been previously described with respect to plate heater 64 of FIGS.1-5. In addition, the number and arrangement of the heating elements 90and channels 66 c depends on the amount of heat required for aparticular application and is not limited to the embodiment shown inFIGS. 8-10.

End caps 96 are provided at ends 98 and 100 of the heater 60 c. Each endcap 96 is coupled to the heater plate body 64 c by fasteners (notshown), which extend through apertures 102. The end caps 96 are providedto distribute the heat from the exposed elbow 92 and terminal end 94portions of the heating elements 90. The plate heater 60 c furtherincludes relief holes 68 c, which are drilled at regular intervals alongthe length of the extruded heater plate body 64 c. The relief holes 68 care provided to receive mechanical items including fasteners (not shown)for coupling the heater 60 c to the manifold.

As shown, the plate heater 60 c includes multiple thermocouple apertures70 c for receiving thermocouples (not shown). Each thermocouple isdedicated to one control zone of the plate heater 60 c. Each controlzone typically controls a maximum heater input of 15 amps. The number ofcontrol zones, and therefore thermocouples, is determined by the desiredheat output for plate heater 60 c. Heating elements 90 may be poweredindependently, in parallel or in series. Powering the heating elements90 independently or in parallel provides a fail-safe, redundantarrangement for the plate heater 60 c. In one embodiment, a parallelarrangement requires fewer control zones and therefore is less costlythan independent control of each heating element 90.

Operation of the plate heater 60 c is similar to operation of plateheaters 60, 60 a, 60 b of the previously described embodiments, andtherefore will not be described further here.

The plate heater 60 c is produced in a similar manner as has beenpreviously described with respect to heater 60 of FIGS. 1-5; however,the profile for the die of plate heater 60 c differs and is shown inFIG. 10A. The profile includes a linear portion 65 c′, which correspondsto contact surface 65 c of the heater plate body 64 c and extendedportion 66 c′, which corresponds to channel 66 c of the heater platebody 64 c. Following extrusion, ends 98, 100 of the heater plate body 64c are machined by a machining operation such as milling or grinding, forexample, to accommodate the terminal ends 94 of the heating elements 90.The heating elements 90 are then positioned in the channels 66 c and maybe deformed to provide three-sided contact with its respective channel66 c, by a technique such as rolling a tool under pressure over theheating elements 90. In accordance with one embodiment of the presentinvention, the rolling or swagging operation flattens the top side ofheating element 90 and maximizes the amount of contact between theremaining three-sides of heating element 90 and its respective channel66 c, in order to optimize the heat transfer therebetween. Othertechniques for deforming the heating elements 90 may alternatively beused.

The heating elements 90 are replaceable by an operator. This provides acost savings, as the entire plate heater 60 does not need to be scrappedand replaced when one or more heating elements fail. In variousembodiments of the present invention, deformation of the heatingelements 90 in the channels 66 c makes it possible for heating elements90 having different diameters to be installed without significantlyreducing the amount of contact between the heating element 90 and thechannel 66 c. In embodiments where heating elements having smallerdiameters are installed, it may be desirable to fill any gaps betweenthe heating element 90 and the channel 66 c with a thermally conductivepaste. The thermally conductive paste does not affect the removal of theheating elements 90 from the channels 66 c and breaks away when theheating elements 90 are removed for repair or replacement.

It will be appreciated by a person skilled in the art that by deformingthe heating elements 90 into the channels 66 c, no additional clampingplate is required so that the heating elements 90 are unenclosed.

Referring to FIGS. 11 and 12, another embodiment of a plate heater 60 dfor a manifold 12 d is shown. In this embodiment, a heater plate body 64d includes a pair of channels 66 d for receiving heating elements 90 d.The channels 66 d are provided in a contact surface 65 d of the heaterplate body 64 d so that upon assembly, the heater elements 90 d contactan upper surface 38 d of the manifold 12 d. This arrangement allows fordirect contact between the heating elements 90 d and the manifold 12 d,therefore providing efficient heat transfer therebetween. A thermallyconductive paste may be included to fill any gaps and increase theamount of contact between the heating element 90 d and the both thechannel 66 d and the manifold 12 d. Apertures 104 are provided forreceiving fasteners (not shown) to fix the plate heater 60 d to themanifold 12 d and clamp the heating elements 90 d to the upper surface38 d.

Although plate heater 60 d is shown coupled to the upper surface 38 d ofthe manifold, it will be appreciated that similar to the previous heaterembodiments, the plate heater 60 d may be coupled to any surface of themanifold 12 d. Further, one channel 66 d or a plurality of channels 66 dmay be provided depending on the amount of heat required for aparticular application.

The heater plate body 64 d may be formed by an extrusion process or acombination of extrusion and machining. The heater plate body 64 d ismade of a suitable material such as those materials previously describedwith respect to plate heater 60 of FIGS. 1-5.

Another embodiment of the present invention is shown in FIGS. 13 and13A. Plate heater 60 e includes an extruded heater plate body 64 ehaving four channels 66 e for receiving four heating elements 90 e in anupper surface 88 e thereof. Although four channels and heating elementsare shown, a fewer or greater number may be employed without departingfrom the scope of the present invention. Channels 66 e and heatingelements 90 e extend the length of heater plate 64 e in parallel witheach other. In contrast to the embodiment shown in cross-section in FIG.10, channels 66 e have a straight-walled, u-shaped cross-section sizedslightly larger than heating element 90 e with a channel depth thatfully receives heating elements 90 e therein. Accordingly, an uppermostpoint of heating elements 90 e sits at or below heater plate body uppersurface 88 e in contact with the walls of channel 66 e to provide foroptimal heat transfer therebetween. Heating element 90 e may be swaged,or otherwise pressed, into channel 66 e to make three-sided contact withheater plate body 64 e. In one embodiment, a top surface of heatingelement 90 e may be flattened during the swaging process. Heatingelements 90 e are thus held in-place within channels 66 e without anadditional cover or clamping arrangement so that they are easilyreplaced if one should fail.

In another embodiment shown in FIG. 13B which is combinable with theembodiment of FIG. 13), channels 66 e may have a groove portion 71 e andan undercut portion 67 e that is a slightly enlarged area below groove71 e, similar to narrowed portion 71 c and enlarged portion 67 c shownin FIG. 10. Heating elements 90 e, each of which has an outer diameterthat is slightly larger than groove portion 71 e but roughly equivalentto undercut portion 67 e, are then pressed through groove portions 71 eto sit within undercut portions 67 e of channel 66 e. In an embodiment,undercut portion 67 e is sized to fully receive and to maintain contactwith heating element 90 e for maximum heat transfer therebetween. Onemethod of making the embodiment of FIG. 13B, includes forming anundersized version of channel 66 e during the extrusion process thatforms heater plate body 64 e, and then machining groove portion 71 e andundercut portion 67 e to a suitable geometry to accommodate heatingelement 90 e as previously described.

Each heating element 90 e includes terminal ends 94 e (one of which isshown in FIG. 13A), and is connected in parallel to or wired independentof at least one other heating element 90 e. Thus, multiple heatingelements 90 e wired in parallel or independently provide redundancy inoperation for heater plate 64 e. Terminal ends 94 e are positionedbetween an upper and lower portion of a respective end cap 110, whichare attached at each end of heater plate 64 e by clamps 112. As inprevious embodiments, one or more heater 60 e may be attached to a top,side and/or bottom surface of the manifold depending on the applicationand heating needs. The end cap 110 comprises four inlets, each alignedwith one of the channels 66 e respectively and receiving a terminal end94 e of a heating element 90 e. The upper and lower portion of the endcap 110 each including a half of four inlet channels 95 e for receivinga straight portion of the terminal ends 94 e. The inlet channels 95 eintersecting a through channel 96 e for receiving bent end portions ofthe terminal ends 94 e. The through channel 96 e having two outlets 97 efrom which the connecting ends 98 e of the terminal ends 94 e project.The upper and the lower portion of the end 110 each including a half ofthe through channel 96 e. The end cap 110 is made out of an electricallyinsulative material that can withstand molding temperatures, preferablya ceramic material.

The end cap 110 is shaped like an extension of the heater plate body 64e and the height h_(c) and the width w_(c) of the end cap 110 are equalor smaller than the height h_(b) and the width w_(b) of the heater platebody 64 e. Due to the fact that not only a straight portion, but also abent portion of the terminal ends 94 e are positioned in the end cap 110forces applied to the connecting ends 98 e do not influence theconnection of the heating element 90 e in the channels 66 e. As with theembodiment shown in FIG. 9 such an end cap 110 could also position notonly terminal ends 94 e, but also the combination of terminal ends 94 eand a conventional bend (like elbow 92 in FIG. 9) or only suchconventional bends. The two halves of the end cap 110 are identical andhaving respective connecting means to be fitted together.

With regard to the materials of the heater plate body 64 e, thearrangements of heating elements and their electrical connection etc. itis referred to the above embodiments. These features and techniques arealso applicable here.

Another embodiment of the present invention is shown in FIG. 14-18. Thisembodiment is similar to the embodiment disclosed in FIG. 13-13B. Thus,only the differences are explained in the following. With regard to theremaining features and aspects it is therefore referred to the above.

This embodiment also includes end caps 110 on both ends of the plateheater 60 f. The height h_(e) of the end cap 110 is smaller than theheight h_(b) of the heater plate body 64 f. Each end cap 110 isconnected to the end of the heater plate body 64 f by using a U-shapedclamp 112 f. Whereas the side face of the end cap 110 including theinlets is pressed against the end face of the heater plate body 64 f thethree other side faces of the end cap 110 are held in the framelikestructure of the U-shaped clamp 112 f. The clamp 112 f does not onlyhave an overall U-shape, but also a U-shape cross-section. So that theend cap 110 can be inserted in this framelike structure provided byclamp 112 f. The legs of the U-shaped clamp 112 f are bolted to theheater plate body 64 f. The clamp 112 f does have side windows 99 fbeing in alignment with the outlets 97 f of the end cap 110 so that theconnecting ends 98 f projecting out of the windows 99 f respectively.The clamp 112 f is preferably made from a steel material.

End caps 110 as described with some of the above embodiments can be usedwith all of the heater designs disclosed.

The many features and advantages of the invention are apparent from thedetailed specification and, thus, it is intended by the appended claimsto cover all such features and advantages of the invention that fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and changes will readily occur to those skilledin the art, it is not desired to limit the invention to the exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope of the invention.

1. A method of manufacturing a heater for a hot runner manifold, themethod comprising: providing an extruded heater plate body having atleast two longitudinally-extending parallel channels therein; machininga flat contact face of the heater plate body; and inserting a heatingelement into each of the channels.
 2. The method of claim 1, whereinterminal end portions of each of the heating elements extends out of therespective channel and further including the step of: providing at leastone end cap for commonly fixing the terminal end portions of the heatingelements relative to the heater plate body.
 3. The method of claim 2,wherein the terminal end portions of the heating elements are bent andthe bends are covered by the end cap.
 4. The method of claim 1, furthercomprising the step of: extruding a bar-like blank having the at leasttwo longitudinally-extending parallel channels formed therein; andcutting the bar-like blank across a width thereof to provide theextruded heater plate body.
 5. The method of claim 4, wherein thechannels have a key-shaped cross-section.
 6. The method of claim 4,wherein the channels are formed within one of a top and bottom surfaceof the heater plate body.
 7. The method of claim 4, wherein the channelsare formed within opposing side surfaces of the heater plate body. 8.The method of claim 1, further comprising: machining ends of the heaterplate body to accommodate installation of the terminal end portions ofthe heating elements.
 9. The method of claim 1, further comprising thesteps of: machining the channels to have a groove portion and anundercut portion, wherein the undercut portion is wider than the grooveportion and sized to be substantially equal to an outer diameter of theheating element to be received therein; and placing the respectiveheating element into contact with the undercut portion of the channel.10. The method of claim 9, wherein inserting the heating element intothe channel includes pressing and deforming the heating element into thegroove in order to maximize contact between the heating element and theundercut portion
 11. A method of manufacturing a heater for a hot runnermanifold, the method comprising: extruding a heater plate from a rawform to a final form using a die, the heater plate including a channel;machining the channel to have a groove portion and an undercut portion,wherein the undercut portion is wider than the groove portion; cuttingthe heater plate to a length based on the configuration of the manifold;and placing a heating element into contact with the undercut portion ofthe heater plate channel, wherein the heater plate is coupled to themanifold for providing heat thereto.
 12. The method of claim 11, furthercomprising; machining a contact surface of the heater plate to maximizecontact between the contact surface and a surface of the manifold. 13.The method of claim 12, further comprising: machining ends of the heaterplate to accommodate installation of heating element terminations. 14.The method of claim 13, further comprising: machining relief holes inthe heater plate, the relief holes being provided to accommodateconnections of other components to the surface of the manifold.
 15. Themethod of claim 11, wherein placing the heating element into the channelincludes pressing and deforming the heating element into the groove inorder to maximize contact between the heating element and the undercutportion.